Method of forming interlayer film

ABSTRACT

A method of forming an interlayer film on a substrate with a plurality of patterns formed thereon wherein the interlayer film is deposited on the substrate by a process comprising a plurality of steps in each of which a portion of the film is deposited so as to have different fluidity with the same source material.

This application is a division of Ser. No. 08/896,542 filed Jul. 18,1997.

BACKGROUND OF THE INVENTION

This invention relates to a method of forming an interlayer film,particularly to a method suited for forming an interlayer insulatingfilm in manufacturing semiconductor devices.

In manufacturing semiconductor devices, a method is often adopted inwhich fluid source materials are used to form interlayer insulatingfilms so as to fill up troughs on a substrate surface formed by wiringpatterns thereon to assure a high smoothness of the substrate surface.When using the fluid source material for forming the interlayerinsulating film, the fluid film, while it is being deposited, flows intothe troughs between patterns from the top surfaces of the wiringpatterns, resulting in filling the troughs.

When forming such an interlayer insulating film, a single step filmdeposition process is carried out in the related method to obtain thedesired film thickness (for example, see M. Matsuura and M. Hirayama,1995 Dry Process Symposium, pp. 261-268 (1995)).

Such a method of forming interlayer insulating films, however, causes anundesirable phenomenon that, when the troughs on the substrate surfaceare formed by a plurality of patterns of differing widths, the thicknessof the film formed on each of those patterns varies with dependence onpattern widths (hereinafter, this phenomenon is referred to as poorglobal smoothness), resulting in differences in level. This isconsidered to be as follows. When the film is deposited, the fluid filmswells on each pattern due to the surface tension. On a wide pattern,the film swells more despite the fluid film flowing into the troughbetween patterns from the edge of the pattern as the film becomesthicker, so that when the film deposition ends, the film is formed witha thickness as swelled and results in becoming thicker than on anarrower pattern.

If an interlayer insulating film has such poor global smoothness, thereoccurs problems such as the step coverage of the formed interlayerinsulating film becoming poor and a wiring layer or the like becomingthin partially when formed on the interlayer insulating film.

In view of foregoing, it is an object of this invention to provide amethod of forming an interlayer film, which can eliminate the abovephenomenon that the film formed on each pattern becomes uneven inthickness due to differences in width of those patterns formed on thesubstrate.

SUMMARY OF THE INVENTION

Above object is achieved by a method of forming an interlayer film inwhich the interlayer film is formed by a process comprising a pluralityof steps in each of which a portion of the film is deposited with thesame source material under a condition of providing the portion of filmwith different fluidity.

In a method of forming an interlayer film according to the first aspectof the present invention, a portion of the interlayer film is at firstdeposited under a condition of providing the portion of film withrelatively reduced fluidity, so that the film is deposited with analmost uniform thickness regardless of any pattern width on thesubstrate. After this, the rest portion of the film is deposited under acondition of providing the rest portion of the film with relativelyincreased fluidity so as to fill up the trough between the patterns.

In a method of forming an interlayer film according to the second aspectof the present invention, an undercoating film is formed in advancewhich affects to reduce fluidity of a portion of the interlayer film tobe formed thereon, by which the portion of the interlayer film isdeposited with an almost uniform thickness regardless of any patternwidth on the substrate. Then, using the same source material, the restportion of the film is deposited over the above portion of the filmunder a condition of providing the rest portion of the film withrelatively increased fluidity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A through FIG. 1C are cross sectional side views of a major partof a semiconductor device for illustrating an embodiment of the presentinvention is successive processing steps.

FIG. 2 is a schematic view showing a configuration of a CVD apparatusappropriately used for embodying the present invention.

FIG. 3A through FIG. 3D are cross sectional side views of a major partof a semiconductor device for illustrating the third embodiment of thepresent invention in successive processing steps.

FIG. 4A through FIG. 4E are cross sectional side views of a major partof a semiconductor device for illustrating the fourth embodiment of thepresent invention in successive processing steps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a method of forming an interlayer film according tothe present invention will be explained in detail with reference to someembodiments.

First Embodiment

This first embodiment is a method of forming an interlayer filmaccording to the first aspect of the present invention and provides aninterlayer film made of an SiO₂ film by two steps of film formingprocesses, which will be explained with reference to FIGS. 1A through1C.

FIG. 1A shows a substrate for forming an interlayer film. A substrate 1is made of a silicon wafer. On this substrate 1 are formed an Al wiringpattern 2 and an Al pad pattern 3 via an oxide film or the like (notillustrated). The Al wiring pattern 2 is formed to be 0.85 μm in heightand 0.4 μm in width. The Al pad pattern 3 is formed to be 0.85 μm inheight and 100 μm in width. Between those Al wiring pattern 2 and Al padpattern 3 is provided an enough space, with which each of those patternsbecomes independent of the other. In FIGS. 1A through 1C, the wiringwidths of the Al wiring pattern 2 and the Al pad pattern 3 areillustrated with different ratios for convenience.

In order to form an interlayer film on the substrate 1, on which areformed the Al wiring pattern 2 and the Al pad pattern 3 of differingwidths, to fill up a trough due to the patterns, an SiO₂ film 4 isformed in a thickness of 0.4 μm using a well-known plasma CVD apparatus,and SiH₄ and H₂ O₂ as source materials at a film deposition temperatureof 30° C. with the SiO₂ film 4 covering the Al wiring pattern 2 and theAl pad pattern 3 as shown in FIG. 1B.

The flow rate of the source material SiH₄ was defined to be 120 sccm. Asfor H₂ O₂, hydrogen peroxide solution of 60% in concentration wasintroduced into the reduced pressure CVD apparatus at a flow rate of0.65 g/min and instantaneously evaporated by a flasher immediately afterbeing introduced to react to SiH₄. As a carrier gas, N₂ was used at aflow rate of 1000 sccm separately from the above mentioned SiH₄ and H₂O₂. The reaction pressure was set at 850 m Torr.

Above described SiH₄ and H₂ O₂ used as source materials satisfy acondition for having fluidity when deposited. Specifically, theirfluidity is reduced at 20° C. or less under the above mentioned flowrate of source material and reaction pressure. Over 30° C., theirfluidity is almost lost. On the other hand, their fluidity is increasedgradually under 20° C. Especially, under 5° C., their fluidity increasessignificantly. Such a deposition temperature dependent fluidity changeis considered to be due to a reaction mechanism of oxidizing SiH₄ intoSi(OH)₄ by an oxidant H₂ O₂ and further dehydrating and condensing theresultant Si(OH)₄ into SiO₂, in which mechanism the process ofdehydrating and condensing Si(OH)₄ nearly in liquid phase, into SiO₂ insolid phase, is accelerated at high temperatures and decelerated at lowtemperatures.

The SiO₂ film 4 formed under such deposition conditions is to be as aportion of the interlayer film in this invention and, because of beingformed at 30° C., the film has almost no fluidity when deposited.Consequently, the film becomes almost even in thickness regardless ofthe widths of the patterns 2 and 3 formed under the film. In this stage,however, the film does not fill up the trough between the patterns 2 and3 yet.

After this, the SiO₂ film 5, which is assumed as the rest portion of theinterlayer film in this invention, is formed on the above mentioned SiO₂film 4 as shown in FIG. 1C in a thickness of 0.4 μm under the sameconditions except for the deposition temperature, which is changed to 0°C. Thus, an interlayer film 6 comprising the SiO₂ film 4 together withthe above SiO₂ film 5 is obtained.

The SiO₂ film 5 formed under such deposition conditions has a highfluidity when deposited as mentioned above because of the depositiontemperature of 0° C., so that the film can fill up the trough formed onthe SiO₂ film 4 due to the patterns 2 and 3. Consequently, theinterlayer film 5 becomes to provide a satisfactory surface smoothness.In other words, since patterns 2 and 3 are already covered by the SiO₂film 4, the SiO₂ film 5 formed on this film comes in contact with theSiO₂ film 4 without coming in direct contact with the narrow Al wiringpatter 2 and the wide Al pad pattern 3 even on the patterns 2 and 3.Thus, the underside of the SiO₂ film 5 is completely occupied with theSiO₂ film 4 which provides a uniform wettability. Thus, unlike therelated art method, the SiO₂ film 5 is not affected by the surfacetension on the patterns but is affected only by gravitation whendeposited. Consequently, the film 5 can fill up the trough by thefluidity of the film and the surface become smooth.

When an SiO₂ film having a thickness of 0.8 μm is formed using SiH₄ andH₂ O₂ as source materials in the state shown in FIG. 1A by a single stepdeposition process without being divided into two steps at a depositiontemperature of 0° C. under the same conditions as mentioned above, thedifference in film thickness between the SiO₂ films on the Al wiringpattern 2 and the Al pad pattern 3 was 400 nm. In this first embodiment,however, this difference in the film thickness could be reduced down to150 nm.

Furthermore, with the method in this first embodiment, the difference infilm thickness between the SiO₂ film on a plurality of the denselyformed Al wiring patterns 2 and the SiO₂ film on a plurality of thedensely formed Al pad patterns 3 could be reduced by 110 nm comparedwith that with the related art method in which a single step depositionprocess is carried out.

As explained above, it is confirmed that this first embodiment is veryeffective for preventing the global smoothness from becoming poor.

In the above embodiment in which the second deposition process iscarried out just after the first one, plasma exposure may be carried outonto the SiO₂ film 4 just after the first deposition process prior tothe formation of the SiO₂ film 5. This plasma exposure hardens theplasma-exposed surface of the SiO₂ film 4, with which the film 4 losesits fluidity almost completely. Thus the SiO₂ film 4 is prevented fromflowing slightly to be affected by the difference in widths of patterns2 and 3 before the second deposition process is carried out.

Second Embodiment

This second embodiment is also a method according to the first aspect ofthe invention and is explained as a method of forming an interlayer filmwith the plasma CVD method and the reduced pressure CVD method as twosteps of deposition processes.

FIG. 2 shows an apparatus that can carry out both plasma CVD method andreduced pressure CVD method. This CVD apparatus 10 is provided with awafer stage 13 in vacuum chamber 12 provided with an exhaust pipe 11connected to a vacuum pump (not illustrated). In the vacuum chamber 12is provided with a pipe 14 used for introducing source materialsspecifically SiH₄, H₂ O₂, and a carrier gas (N₂) from a source materialsupply (not illustrated). To this pipe 14 is connected a shower head 15above the wafer stage 13 in the vacuum chamber 12, with the shower head15 facing the wafer stage 13. An RF oscillator 16 is connected to thisshower head 15 so that plasma is generated between this shower head 15and the wafer stage 13.

To carry out deposition of a film on a wafer W (substrate 1) on whichthe Al wiring pattern 2 and the Al pad pattern 3 are formed as shown inFIG. 1A by using such a configuration of the CVD apparatus, at first thewafer W is set on the wafer stage 13 as shown in FIG. 2, and in thisstate, the vacuum pump is started to evacuate the vacuum chamber 12 tothe specified pressure. Then, the temperature of the wafer W is adjustedto 0° C. and an RF power is applied to between the shower head 15 andthe wafer stage 13 by the RF oscillator 16 to generate plasma.

The source material is then introduced into plasma P through the showerhead 15 from the pipe 14 for reaction to form an SiO₂ film as shown inFIG. 1B. (Although the SiO₂ film formed in this second embodimentdiffers from the SiO₂ film formed in the first embodiment, a numeral 4is also assigned to the SiO₂ film formed in this second embodiment forconvenience of the substrate explanation.)

The flow rates of SiH₄ and H₂ O₂ as source materials, as well as N₂ as acarrier gas were set to 120 sccm, 0.65 g/min, and 1000 sccm,respectively. The deposition pressure was set at 850 m Torr.

Since the SiO₂ film 4 thus formed under such deposition conditions isassumed as a portion of the interlayer film in this invention and thefilm is formed with the plasma CVD method, the film does not flow whendeposited. Consequently, the film becomes almost even in thicknessregardless of the widths of the patterns 2 and 3 formed under the film.In this stage, however, the film cannot fill up the trough between thepatterns 2 and 3 yet. Like the case in the first embodiment.

Subsequently, introduction of the material is stopped, and applicationof RF power by the RF oscillator 16 is stopped to extinguish the plasmain the vacuum chamber 12.

After this, an SiO₂ film 5 to be assumed as the rest portion of theinterlayer film in this invention as shown in FIG. 1C is formed on theSiO₂ film 4 without plasma generation in a thickness of 0.4 μm under thesame conditions as those of the preceding deposition. Thus, theinterlayer film 6 comprising the SiO₂ film 4 and 5 is obtained.(Although the SiO₂ film and the interlayer film formed in this secondembodiment differ from the SiO₂ film 5 and the interlayer film 6 formedin the first embodiment, numerals 5 and 6 are respectively assigned alsoto the SiO₂ film and the interlayer film formed in this secondembodiment for convenience.)

Thus formed SiO₂ film 5, being deposited under a temperature of 0° C.,has high fluidity when deposited, so that it can fill up the troughformed on the surface of the SiO₂ film 4 due to the Al wiring pattern 2and the Al pad pattern 3 like in the first embodiment. Consequently, theinterlayer film 5 is formed to have a satisfactory smoothness.

When an SiO₂ film having a thickness of 0.8 μm is formed using SiH₄ andH₂ O₂ as source materials in the state shown in FIG. 1A by a single stepdeposition process without being divided into two steps at a depositiontemperature of 0° C. under the same conditions as mentioned above, thedifference in film thickness between the SiO₂ films on the Al wiringpattern 2 and the Al pad pattern 3 was 400 nm as mentioned above, but inthis second embodiment, this difference in film thickness could bereduced down to 170 nm.

Furthermore, with the method in this second embodiment, the differencein film thickness between the SiO₂ film on a plurality of the denselyformed Al wiring patterns 2 and the SiO₂ film formed on a plurality ofthe densely formed Al pad patterns 3 could be reduced by 100 nm comparedwith that with the related art method in which a single step depositionprocess is carried out.

As explained above, it is confirmed that this second embodiment is alsovery effective for preventing the global smoothness from being poor.

Furthermore, in the first and second embodiments, SiH₄ and H₂ O₂ areused as source materials, but the materials are not limited to them inthis invention. For example, instead of SiH₄, Si₂ H₆ and the like may beused, and, instead of H₂ O₂, an oxidizer dissolved in water such asozone (O₃) dissolved in water or, furthermore, liquid nitrogen and thelike may be used.

In the first and second embodiments, two steps deposition process arecarried out to form the desired interlayer film 6. The depositionprocess, however, may be carried out by more than three steps forobtaining the interlayer film 6 by carrying out the first depositionprocess under a condition basically to reduce the fluidity or preventthe fluidization, and then the subsequent deposition processes under acondition to increase the fluidity.

Furthermore, in the first embodiment, fluidity is adjusted by changing adeposition temperature which is adopted as a deposition condition toreduce or increase the fluidity. However, the fluidity may also beadjusted by changing the deposition pressure, the mixing rate of thesource materials, etc.

Third Embodiment

This third embodiment explains a method of forming an interlayer filmaccording to the second aspect of the invention and provides theinterlayer film made of an SiO₂ film on an undercoating film by twosteps of film forming processes, which will be explained with referenceto FIGS. 3A through 3D.

FIG. 3A shows a substrate for forming an interlayer film. A substrate 1is made of a silicon wafer. On this substrate 1 are formed an Al wiringpattern 2 and an Al pad pattern 3 via an oxide film or the like (notillustrated). The Al wiring pattern 2 is formed to be 0.85 μm in heightand 0.4 μm in width. The Al pad pattern 3 is formed to be 0.85 μm inheight and 100 μm in width. Between those Al wiring pattern 2 and Al padpattern 3 is provided an enough space, with which each of those patternsbecomes independent of the other. In FIGS. 3A through 3D, the wiringwidths of the Al wiring pattern 2 and the Al pad pattern 3 areillustrated with different ratios for convenience.

In order to form an interlayer film on the substrate 1, on which areformed the Al wiring pattern 2 and the Al pad pattern 3 of differingwidths, to fill up a trough due to the patterns, an undercoating film isat first formed before forming the interlayer film. In this embodiment,a P-TEOS.SiO₂ film 4 (undercoating film) is deposited in a thickness of0.1 μm with the P-TEOS.SiO₂ film 4 covering the Al wiring pattern 2 andthe Al pad pattern 3 with a plasma CVD method using a well-known plasmaCVD apparatus, and using TEOS (tetraethoxysilane) as a source materialat a film deposition temperature of 400° C. as shown in FIG. 3B.

Subsequently, the surface of this P-TEOS.SiO₂ film 4 is treated withhydroxylamine (NH₂ OH), which is a powerful reducing agent. Then, theSi--O bonds of the P-TEOS.SiO₂ film 4 are cut by the reductiontreatment, so that the surface becomes hydrophobic.

Subsequently, on the hydrophobic surface of the P-TEOS.SiO₂ film 4 isformed an SiO₂ film 5 (a portion of an interlayer film in thisinvention) with the SiO₂ film 5 covering both of the Al wiring pattern 2and the Al pad pattern 3 as shown in FIG. 3C. The SiO₂ film 5 wasdeposited at a film-deposition temperature of 0° C. using a well-knownreduced pressure CVD apparatus and using SiH₄ and H₂ O₂ as sourcematerials so as to obtain the SiO₂ film with a thickness of 0.4 μm.

The flow rate of the source material SiH₄ was defined to be 120 sccm. Asfor H₂ O₂, hydrogen peroxide solution of 60% in concentration wasintroduced into the reduced pressure CVD apparatus at a flow rate of0.65 g/min and instantaneously evaporated by a flasher immediately afterbeing introduced to react with SiH₄. As a carrier gas, N₂ was used at aflow rate of 1000 sccm separately from the above mentioned SiH₄ and H₂O₂. The reaction pressure was set at 850 m Torr.

Above described SiH₄ and H₂ O₂ used as source materials satisfy acondition for having fluidity when deposited. Specifically, theirfluidity increases at 20° C. or less under the above mentioned flow rateof source material and reaction pressure. Especially, under 5° C., theirfluidity increases significantly. Above 20° C., their fluidity decreasesand over 30° C., their fluidity is almost lost.

Consequently, in this embodiment, the obtained SiO₂ film 5, although itintrinsically exhibits its fluidity when deposited because of beingdeposited at 0° C., is prevented from exhibiting its fluidity since thehydrophobization treatment is provided in advance on the surface of theP-TEOS.SiO₂ film 4 as the undercoating film. This makes the SiO₂ film 5almost even in thickness regardless of the widths of the Al wiringpattern 2 and the Al pad pattern 3. Consequently, in this stage, theSiO₂ film 5 formed as a portion of an interlayer film in the inventionis prevented from exhibiting its fluidity to have poor smoothness. Thus,the trough formed between the Al wiring pattern 2 and the Al pad pattern3 is not yet satisfactorily filled up.

Subsequently, the substrate 1 on which the SiO₂ film 5 is formed istransferred into another chamber for plasma treatment. In this chamber,the substrate 1 is heated up to 350° C. and, in this state, an oxygenplasma treatment is applied to the SiO₂ film 5 for one minute. Aftersuch a plasma exposure, the exposed surface of the SiO₂ film 5 ishardened and loses its fluidity almost completely to prevent the SiO₂film 5 from such slight flowing that causes the film to be affected by adifference of width between patterns 2 and 3 before the second filmdeposition is applied. Furthermore, this plasma exposure can alsoincrease the hydrophilic nature of the SiO₂ film 5 itself, since theexposure eliminates fluidity of the film as well as reduces the watercontent in the SiO₂ film 5.

After this, the plasma treated substrate 1 is returned into the originalchamber of the reduced pressure CVD apparatus and an SiO₂ film 6 assumedas the rest portion of the interlayer film in this invention is formedon the above mentioned SiO₂ film 5 as shown in FIG. 3D in a thickness of0.4 μm under the same conditions as those of depositing the SiO₂ film 5so as to obtain an interlayer film 7 comprising an SiO₂ film togetherwith the above SiO₂ film 5.

The SiO₂ film 6 thus formed has a high fluidity when deposited asmentioned above because of the deposition temperature of 0° C., so thatthe film can fill up the trough formed on the surface of the SiO₂ film 5due to the Al wiring pattern 2 and the Al pad pattern 3. Consequently,the interlayer film 7 becomes to have a satisfactory smoothness. Inother words, since patterns 2 and 3 are already covered by the SiO₂ film5, the SiO₂ film 5 to be formed on this film comes in contact with theSiO₂ film without coming in contact with the P-TEOS.SiO₂ film 4 directlyeven on the narrow Al wiring pattern 2 and the wide Al pad pattern 3.Thus, the underside of the SiO₂ film 6 is completely occupied with theSiO₂ film 5 which provides a uniform wettability together with anincreased hydrophilic nature due to the plasma exposure. Hence, unlikethe related art method, the SiO₂ film 6 is not affected by the surfacetension on the patterns but is affected only by gravitation whendeposited. Consequently, the film 6 can fill up the troughs by thefluidity of the film and the surface becomes smooth.

When an SiO₂ film having a thickness of 0.8 μm is formed with SiH₄ andH₂ O₂ as source materials in the state shown in FIG. 3A by a single stepdeposition process without being divided into two steps at a depositiontemperature of 0° C. under the same conditions as mentioned above, thedifference in film thickness between the SiO₂ films on the Al wiringpattern 2 and the Al pad pattern 3 was 400 nm. In this third embodiment,however, this difference in film thickness could be reduced down to 160nm.

Furthermore, with the method in this third embodiment, the difference infilm thickness between the SiO₂ film (interlayer film 7) on a pluralityof the densely formed Al wiring patterns 2 and the SiO₂ film (interlayerfilm 7) on a plurality of the densely formed Al pad patterns 3 could bereduced by 110 nm compared with that with the related art method inwhich a single step deposition process is carried out.

As explained above, it is confirmed that this third embodiment is veryeffective for preventing the global smoothness from becoming poor.

In the above embodiment, plasma exposure was carried out after the firstfilm deposition. However, the second film deposition may be carried outwithout performing the plasma exposure.

Fourth Embodiment

This fourth embodiment is also a method of forming an interlayer filmaccording to the second aspect of the invention and provides theinterlayer film comprising an SiO₂ film on an undercoating film by twosteps of film deposition processes, which will be explained withreference to FIGS. 4A through 4E.

FIG. 4A is a view showing a substrate for forming an interlayer film.Like in FIG. 1A or FIG. 3A, on the substrate 1 made of a silicon waferare formed an Al wiring pattern 2 and an Al pad pattern 3 via an oxidefilm or the like (not illustrated). Since those substrate 1, Al wiringpattern 2, and Al pad pattern 3 are the same as those in FIG. 1A or FIG.3A, detailed explanation for them will be omitted here.

In order to form an interlayer film on the substrate 1, on which areformed an Al wiring pattern 2 and an Al pad pattern 3 of mutuallydiffering widths, to fill up the trough due to the above mentionedpatterns, a P-TEOS.SiO₂ film 4 (undercoating film) is deposited in athickness of 0.1 μm as shown in FIG. 3B before forming the interlayerfilm like the case in the third embodiment.

Then, on this P-TEOS.SiO₂ film 4 is deposited a hydrogenated amorphoussilicon film (a-Si: H film) 11 in a thickness of 10 nm at a depositiontemperature of 300° C. with SiH₄ as a source material as shown in FIG.4C. The surface of thus obtained amorphous silicon film 11 exhibitshydrophobic nature when deposited.

Subsequently, on the surface of this amorphous silicon film 11 isdeposited an SiO₂ film (a portion of an interlayer film 12 in theinvention) in a thickness of 0.4 μm, covering the Al wiring pattern 2and the Al pad pattern 3 as shown in FIG. 4D. The deposition of thisSiO₂ film 12 is carried out under the same conditions as those of theSiO₂ film 5 in the first embodiment.

Thus obtained SiO₂ film 12 is prevented from exhibiting its fluiditysince the surface of the amorphous silicon film 11 deposited on theP-TEOS.SiO₂ film 4 as an undercoating film in advance exhibitshydrophobic nature. This makes the SiO₂ film 12 almost even in thicknessregardless of the widths of the Al wiring pattern 2 and the Al padpattern 3. Consequently, the SiO₂ film 12 formed as a portion of aninterlayer film in this invention is prevented from exhibiting itsfluidity like the case in the third embodiment to have poor smoothness.Thus, the trough formed between the Al wiring pattern 2 and the Al padpattern 3 is not yet satisfactorily filled up in this stage.

After this, like in the third embodiment, the substrate 1 on which theSiO₂ film 12 is formed is transferred into another chamber for plasmatreatment. In the chamber the substrate 1 is heated up to 350° C. and,in this state, an oxygen plasma treatment is applied to the SiO₂ film 12for one minute.

After this, the plasma treated substrate 1 is returned into the originalchamber of the reduced pressure CVD apparatus and an SiO₂ film 13assumed as the rest portion of the interlayer film in this invention isformed on the above mentioned SiO₂ film 12 as shown in FIG. 4E under thesame conditions as those of depositing the SiO₂ film 12 in a thicknessof 0.4 μm to obtain an interlayer film 14 comprising the SiO₂ filmtogether with the above SiO₂ film 12.

Thus formed SiO₂ film 13, being deposited under a temperature of 0° C.so as to have high fluidity when deposited, can fill up the troughformed on the surface of the SiO₂ film 12 due to the Al wiring pattern 2and the Al pad pattern 3 like the case in the third embodiment.Consequently, the interlayer film 14 is formed to have a satisfactorysmoothness. In other words, since patterns 2 and 3 are already coveredby the Si₂ film 2, the SiO₂ film 13 to be formed on the film 12 comes incontact with the SiO₂ film 12 without coming in contact with theamorphous silicon film 11 directly even on the narrow Al wiring pattern2 and the wide Al pad pattern 3. Thus, the SiO₂ film 13 is completelyoccupied with the SiO₂ film 12 thereunder which provides a uniformwettability together with an increased hydrophilic nature due to theplasma exposure. Consequently, unlike the prior art method, the film 13is not affected by the surface tension on the patterns when depositedand accordingly the film 13 can be filled in the troughs due to itsfluidity to be smoothed like the case in the first embodiment.

When an SiO₂ film having a thickness of 0.8 μm is formed using SiH₄ andH₂ O₂ as source materials in the state shown in FIG. 4A by a single stepdeposition process without being divided into two steps at a depositiontemperature of 0° C. under the same conditions as mentioned above, thedifference in film thickness between the SiO₂ films on the Al wiringpattern 2 and the Al pad pattern 3 was 400 nm as mentioned above, but inthis third embodiment, this difference in film thickness could bereduced down to 160 nm.

Furthermore, with the method in the third embodiment, the difference infilm thickness between the SiO₂ film (interlayer film 14) on a pluralityof the densely formed Al wiring patterns 2 and the SiO₂ film (interlayerfilm 14) on a plurality of the densely formed Al pad patterns 3 could bereduced by 110 nm compared with that with the related art method inwhich a single step deposition process is carried out.

As explained above, it is confirmed that this second embodiment is alsovery effective for preventing the global smoothness from being poor.

In the above embodiment, plasma exposure was carried out after the firstfilm deposition, but the second film deposition may be carried outwithout performing the plasma exposure.

Furthermore, instead of the amorphous silicon film 11, a similarlyhydrophobic polysilicon film may be deposited on the P-TEOS.SiO₂ film 4.

Fifth Embodiment

This fifth embodiment is also a method of forming an interlayer filmaccording to the second aspect of the invention and provides theinterlayer film comprising an SiO₂ film on an undercoating film by twosteps film deposition process. It is different from the third embodimentshown in FIGS. 3A through 3D in that the SiO₂ film 5 is formed after theformation of the P-TEOS.SiO₂ film 4 as a hydrophobic undercoating filmwith the hydrophobic nature of the formed P-TEOS.SiO₂ film 4 beingretained, instead of carrying out the reduction treatment for the film4.

In other words, in this embodiment, after the P-TEOS.SiO₂ film 4 isformed as shown in FIGS. 3B, the substrate 1 is transferred into achamber of the reduced pressure CVD apparatus with the vacuum pressurein depositing the P-TEOS.SiO₂ film 4 being maintained so that thehydrophobic nature of the P-TEOS.SiO₂ film 4 is retained. Then, theP-TEOS.SiO₂ film 4, which becomes hydrophobic due to many dangling bonds(unjoined bonds) existing on the surface immediately after thedeposition, can retain its hydrophobic nature because the substrate 1 isheld in vacuum while being transferred into a chamber of the reducedpressure CVD apparatus.

Consequently, the SiO₂ film 5, being formed under the same conditions asthose in the case shown in FIG. 3C with the P-TEOS.SiO₂ film 4 thusretaining its hydrophobic property, is prevented from exhibiting itsfluidity and accordingly the film thickness becomes almost evenregardless of the widths of the Al wiring pattern 2 and the Al padpattern 3. Thus, like the case in the third embodiment, the SiO₂ film 5has poor smoothness and accordingly does not fill up the trough betweenthe Al wiring patter 2 and the Al pad pattern 3 yet in this stage.

Subsequently, the surface of the SiO₂ film 5 is exposed to a plasma likein the first embodiment, aid then the SiO₂ film 6 is formed in athickness of 0.4 μm under the same film deposition conditions as thosein the first embodiment to obtain an interlayer film 7.

Thus formed SiO₂ film 6, being deposited at a temperature of 0° C. so asto increase its fluidity, can fill up the trough formed between the Alwiring pattern 2 and the Al pad pattern 3 on the surface of the SiO₂film 5 like the case in the third embodiment. Consequently, theinterlayer film 7 is formed to have a satisfactory smoothness. In otherwords, since patterns 2 and 3 are already covered by the SiO₂ film 5,the SiO₂ film 6 to be formed on the film 5 comes in contact with theSiO₂ film 5 without coming in contact with the P-TEOS.SiO₂ film 4directly even on the narrow Al wiring pattern 2 and the wide Al padpattern 3. Thus, the underside of the SiO₂ film 6 is completely occupiedwith the SiO₂ film 5 which provides a uniform wettability together withan increased hydrophilic nature due to the plasma exposure. Therefore,unlike the related art method, the film 6 is not affected by the surfacetension on the patterns when deposited and, like the case in the thirdembodiment, the film 6 can fill up the troughs due to its fluidity tosmooth the surface.

When an SiO₂ film having a thickness of 0.8 μm is formed using SiH₄ andH₂ O₂ as source materials in the state shown in FIG. 3A by a single stepdeposition process without being divided into two steps at a depositiontemperature of 0° C. under the same conditions as mentioned above, thedifference in film thickness between the SiO₂ films on the Al wiringpattern 2 and the Al pad pattern 3 was 400 nm as mentioned above. Inthis third embodiment, however, this difference in film thickness couldbe reduced down to 180 nm.

Furthermore, with the method in this fifth embodiment, the difference infilm thickness between the SiO₂ film (interlayer film 7) on a pluralityof the densely formed Al wiring patterns 2 and the SiO₂ film (interlayerfilm 7) formed on a plurality of the densely formed Al pad patterns 3could be reduced by 120 nm compared with that with the related artmethod in which a single step deposition process is carried out.

As explained above, it is confirmed that this fifth embodiment is alsovery effective for preventing the global smoothness from becoming poor.

In the above embodiment, plasma exposure was carried out after the firstfilm deposition, but the second film deposition may be carried outwithout performing the plasma exposure.

Furthermore, in the third, fourth, and fifth embodiments, SiH₄ and H₂ O₂are used as source materials, but the materials are not limited to themin this invention. For example, instead of SiH₄, Si₂ H₆ and the like maybe used, and, instead of H₂ O₂, an oxidizer dissolved in water such asozone (O₃) dissolved in water or, furthermore, oxygen and the like maybe used.

As explained above, in the method of forming the interlayer filmaccording to the first aspect of the present invention, since the firstfilm deposition is carried out under a condition to reduce the fluidityor prevent fluidization, the obtained film (a portion of an interlayerfilm) becomes almost even in thickness regardless of the widths ofpatterns. Furthermore, since the rest portion of the interlayer film isformed on this film under a condition to increase the fluidity whendeposited, this rest portion fills up the trough between patterns.Consequently, the interlayer film comprising the above mentioned portionof the interlayer film and this rest portion becomes to havesatisfactory smoothness even on patterns of differing widths.

the method of forming the interlayer film according to the second aspectof the present invention, an undercoating film is formed on the surfaceof a substrate, then a portion of an interlayer film is formed after theundercoating film is reduction treated so as to become hydrophobic orafter a polysilicon film or an amorphous silicon film is deposited onthe undercoating film, or with the hydrophobic nature of theundercoating film being retained, so that the obtained film (a portionof the interlayer film) becomes almost even in thickness regardless ofthe widths of wiring patterns. And, since the rest portion of theinterlayer film is formed on this film, the rest portion fills up thetrough between wiring patterns, with which the interlayer filmcomprising the above mentioned portion and this rest portion becomes tohave satisfactory smoothness even on wiring patterns of differingwidths.

According to the present invention, therefore, with such a simpleprocess as to combine a plurality of film deposition steps, occurrenceof a phenomenon that a thickness of a film deposited on a patterndiffers with dependence on a pattern width on the substrate (poor globalsmoothness) can be suppressed compared with a case in which a singlelayer film is deposited by the same thickness. This can prevent problemssuch as the step coverage of the formed interlayer film becoming poorand a wiring layer etc. becoming thin partially when formed on theinterlayer film.

What is claimed is:
 1. A method of forming an interlayer film comprisingthe steps of:forming a hydrophobic undercoating film, on a surface of asubstrate, said surface of said substrate having a plurality of patternsof mutually differing widths formed thereon; forming a first interlayerfilm on said hydrophobic undercoating film; and forming a secondinterlayer film on said first interlayer film with the same sourcematerial as that of said first interlayer film.
 2. A method of formingan interlayer film as defined in claim 1, wherein said method furthercomprises the step of exposing said first interlayer film to plasma,said step being carried out between said forming said first interlayerfilm and said forming said second interlayer film.
 3. A method offorming an interlayer film as defined in claim 1, wherein said first andsecond interlayer films are formed by using SiH₄ and H₂ O₂ as the sourcematerials.
 4. A method of forming an interlayer film as defined in claim1, wherein said first and second interlayer films are formed by usingSiH₄, and O₃ dissolved in water as the source materials.